Geologij of the St. Croix Dalles. — Berkey. 378 
by Norton* under the name Basal sandslone is the most ac- 
ceptable yet offered. But the fact that this formation, instead 
of being uniform as the name would indicate, is made up of a 
succession of separable subdivisions, makes a slight modifica- 
tion of the term advisable. The term St. Croix series is a 
much better name, but as restricted by Winchell.f was not 
originally proposed for the whole group of rocks now under 
discussion and has not been uniformly applied by writers. 
Accordingly the term Basal sandstone series has been deter- 
mined upon as a convenient name. It is intended as the co- 
ordinate of Maynesiaa series as used by Hall and Sardeson.;]; 
A prevailingly arenaceous character gives this basal forma- 
tion a unity similar to that secured in the Matjnesian series 
by its dfilomitic development. 
This series of sandstones, shales and conglomerates between 
the base of the overlying St. Lawrence formation and the Ke- 
weenawan floor, exhibits certain characters sufficiently con- 
stant to merit subdivision into at least three distinct parts. 
The uppermost subdivision is a sandstone exhibiting two 
phases: (a) an incoherent fine sand, which is underlain, (b) 
by more compact and thick-bedded layers. Thin seams of 
green shale occasionally appear in tliis bed. Its thickness 
is about 100 feet at its most favorable exposure. Fossils are 
not well preserved within it, and they are not abundant except 
in one horizon. Because of the exceptionally fine exposures 
of this formation in the vicinity of the small village of Fran- 
conia, this uppermost division of the series is called the Fron- 
eonia sandstone. 
The second subdivision has a persistently shaly develop- 
ment in its uppermost and lowest members, between which is a 
green-sand bed, which is coarsely arenaceous. A typical 
section exhibits, in descending order: 
Shaly sandstone, 10 feet. 
Green-.sand, 20 feet. 
Gray shales, 40 feet, to the river, below which its extent 
is unknown. 
The green-sand is a glauconitic mixture. Broken frag- 
*Geol. of Iowa, vol. vr, 1897, p. 140. 
tGeol. and Nat. Hist. Survey, Final Report, vol. ii, 1888, p. xxi. 
+ Bull. Geol. Soc. of America, vol. G, 1895, pp. 167-198. 
